JPS62173857A - Control circuit for video blanking pulse width - Google Patents

Abstract

PURPOSE:To prevent the blanking interruption of signals such as a VIT signal and a character one and the omission of some part of then by detecting a change in the frequency of a horizontal synchronizing signal and changing the blanking pulse width in accordance with the detection output. CONSTITUTION:The DC output E1 of the horizontal synchronizing signal 1 detected from a composite synchronizing signal is outputted through a frequency- voltage converter 2 and an LPF 3. Level detectors (I) and (II) detect the change in the DC output E1 as changes in frequencies f1 and f2, and the detection output is applied to a decoder (binary - ternary) 9. In sorts out the detection output of the level detector into three frequency bands to obtain switching outputs 10, 11 and 12. A switching signal output detection circuit 13 detects the switching outputs 10-12, which are inputted to a blanking width control circuit 14. Thus a vertical blanking pulse is controlled and eventually the vertical blanking pulse corresponding to the pulse width of the vertical blanking pulse is generated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a video blanking pulse width control circuit that controls the pulse width of a video blanking pulse in accordance with changes in the frequency of a horizontal synchronizing signal.

[Prior Art] The horizontal scanning frequency in NTSC color television broadcasting is 15.75 KHz, and the vertical scanning frequency is:
60Hz = Horizontal scanning frequency in high-density broadcasting such as CAPTAINS is 15.75kHz at level A, vertical scanning frequency is 60Hz, horizontal scanning frequency is 31.5kHz at level B = vertical scanning frequency is 60Hz, and The horizontal scanning frequency number in communication using a personal computer is 15 to 33K.
The horizontal scanning frequency and the vertical scanning frequency differ depending on each broadcast or communication, such as 40 to 80 Hz.

When receiving the above broadcasts or communications on the same television receiver (g1), when the horizontal scanning frequency changes, a vertical output circuit is used that inputs the horizontal pulse from the horizontal output circuit via a pump-up circuit. In this case, the pulse width of the vertical retrace pulse fluctuates, and the pulse width of the vertical blanking pulse fluctuates accordingly, and these must be controlled in correspondence with each other.

[Problems to be Solved by the Invention] In the conventional video blanking pulse width control circuit, even if the pulse width of the vertical retrace pulse changes and the pulse width of the vertical blanking pulse changes accordingly, it is difficult to control the pulse width of the vertical blanking pulse. They were not controlled in response to each other.

However, if, for example, the horizontal scanning frequency increases, the pulse width of the vertical retrace pulse becomes narrower, and the pulse width of the vertical blanking pulse is not controlled accordingly.
There have been problems such as so-called retrace disturbances such as vertical retrace interval test (VIT) signals and character signals, and parts of such signals being dropped.

This invention was made to solve the above-mentioned problems, and it is an object of the present invention to obtain a video blanking pulse width control circuit that does not cause retrace interference of VIT signals, character signals, etc., or partial loss of signals. With the goal.

[Means for Solving the Problems] The video blanking pulse width control circuit according to the present invention includes a horizontal synchronizing signal detecting means for detecting a horizontal synchronizing signal from a composite synchronizing signal, and a horizontal synchronizing signal detected by the horizontal synchronizing signal detecting means. a frequency change detection means for detecting a change in the frequency of the horizontal synchronization signal by dividing it into a plurality of frequency bands; a vertical output circuit that receives a horizontal output pulse from the horizontal output circuit and outputs it as a vertical output via a pump-up circuit; vertical synchronization signal detection means for detecting a vertical synchronization signal from the composite synchronization signal;
Vertical blanking pulse generation means receives the vertical synchronization signal detected by the vertical synchronization signal detection means and generates a vertical blanking pulse via a vertical oscillation circuit, and vertical blanking generated by the vertical blanking pulse generation means A blanking pulse width control means is provided for controlling the pulse width of the pulse by changing it according to a plurality of frequency bands detected by the frequency change detection means.

[Function] In the video blanking pulse width control circuit of the present invention, when the frequency of the horizontal synchronizing signal changes, the frequency change detecting means detects this by dividing it into a plurality of frequency bands, and outputs this detection output as a blanking signal. The ranking pulse width is inputted to the ranking pulse width control means, and the pulse width of the vertical blanking pulse generated by the vertical blanking pulse generation means is controlled in accordance with the change in frequency.

[Example] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the video blanking pulse width control circuit of the present invention.

In the figure, reference numeral 1 denotes a horizontal synchronizing signal, which is detected from a composite synchronizing signal by a horizontal synchronizing signal detecting means at the previous stage. 2 is a frequency-voltage converter (F/V converter) for converting the horizontal synchronization signal 1 into a predetermined voltage, 3 is a low-pass filter (LPF), and 4 is for controlling the oscillation of the horizontal oscillation circuit 5. This is an oscillation control circuit.

6 is an AFC that receives the horizontal pulse from the horizontal output circuit 7 and the horizontal synchronizing signal 1 and performs phase comparison by phase detection.
A circuit 8 is a frequency change detecting means, which detects the change in the DC output E1 that has passed through the low-pass filter 3 at frequencies f, , f2.
The level detectors (1) and (II) detect the change (Hi), and input this detection output to the decoder 9.
For example, switching outputs 10, 11, and 12 divided into three frequency bands are obtained.

The switching outputs 10, 11, and 12 are input to the horizontal output circuit 7, and are also input to the blanking width control circuit 14 via the switching signal output detection circuit 13.

15 is a vertical output circuit which boosts the horizontal pulse 16 from the horizontal output circuit 7 via a pump-up circuit 17 and uses it as a driving power source to reduce loss.

This vertical output circuit 15 inputs the vertical synchronization signal 18 detected from the composite synchronization signal through one vertical oscillation circuit, and the one vertical oscillation circuit receives the vertical synchronization signal 18 from the blanking width control circuit 14. A vertical blanking pulse 20 is generated in response to the control output, and this vertical blanking pulse 20 becomes a video blanking pulse 21.

The operation of the video blanking pulse width control circuit configured as described above will be explained below.

The horizontal synchronizing signal 1 detected from the composite synchronizing signal by the horizontal synchronizing signal detecting means becomes a DC output E1 via a frequency-voltage converter 2 and a low-pass filter 3. Changes in this DC output E1 are calculated by frequency f1° f2. The level detectors (I) and (n) detect the change in the level.

This level detector (I) changes from a high level to a low level when, for example, the frequency f of the horizontal synchronizing signal becomes higher than a preset reference frequency f. (II) is a detector that changes from high level to low level when the frequency f of the horizontal synchronizing signal becomes higher than the preset reference frequency f2, and this level detector (I> ,
The detection output of (II) is sent via the decoder 9 to, for example,
Switching outputs 10, 11° and 12 divided into three frequency bands are obtained.

The above switching outputs 10, 11, and 12 are detected by the switching signal output detection circuit 13, and are detected by the blanking width control circuit 14.
is input.

Therefore, in the vertical output circuit 15 to which the pump-up circuit 17 is added, the pulse width of the vertical retrace pulse is set to the switching output 1.
0,11.12, but the vertical oscillation circuit 19
is controlled via the blanking width control circuit 14 according to the frequency band of the switching output 10° 11.12 detected by the switching signal output detection circuit 13, and as a result, the pulse width of the vertical retrace pulse A vertical blanking pulse is generated according to the vertical blanking pulse.

As a result of the above, the retrace interference of VIT signals, character signals, etc. that occurred in conventional video blanking pulse width control circuits,
Partial signal loss will no longer occur.

In the above embodiment, two level detectors (1) and (II) and a decoder 9 are used as the frequency change detecting means 8, and the structure is configured to obtain three switching outputs 10, 11°12. However, the present invention is not limited to these configurations, but any configuration that can detect changes in the horizontal frequency by dividing them into a plurality of frequency bands and obtain detection outputs may be used.

[Effects of the Invention] As explained above, the video blanking pulse width control circuit of the present invention adjusts the pulse width of the vertical blanking pulse for each of a plurality of frequency bands in response to changes in the horizontal frequency of the horizontal synchronization signal. Since it can be controlled, there are excellent effects such as no retrace interference of VIT signals, character signals, etc., and no partial loss of signals.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a video blanking pulse width control circuit showing an embodiment of the present invention. 1...Horizontal synchronization signal, 2...Frequency-voltage converter,
3...Low pass filter, 4...Oscillation control circuit, 5
... horizontal oscillation circuit, 6 ... AFC circuit, 7 ... horizontal output circuit, 8 ... frequency change detection means, 9 ... decoder, 10.11.12 ... switching output, 13.・・・
Switching signal output detection circuit, 14...Blanking width control circuit, 15...Vertical output circuit, 16...Horizontal pulse, 17...Pump up circuit, 18...Vertical synchronizing signal, one . . . Vertical oscillation circuit, 20 . . . Vertical blanking pulse, 21 . . . Video blanking pulse.

Claims (1)

[Claims] horizontal synchronization signal detection means for detecting a horizontal synchronization signal from a composite synchronization signal; and frequency change detection means for detecting changes in the frequency of the horizontal synchronization signal detected by the horizontal synchronization signal detection means by classifying them into a plurality of frequency bands. , a vertical output circuit that receives a horizontal output pulse from the horizontal output circuit and outputs it as a vertical output via a pump-up circuit; a vertical synchronization signal detection means for detecting a vertical synchronization signal from the composite synchronization signal; and a vertical synchronization signal. Vertical blanking pulse generation means that inputs the vertical synchronization signal detected by the detection means and generates a vertical blanking pulse via a vertical oscillation circuit, and the pulse width of the vertical blanking pulse generated by this vertical blanking pulse generation means. 1. A video blanking pulse width control circuit comprising blanking pulse width control means for changing and controlling a plurality of frequency bands according to a plurality of frequency bands detected by the frequency change detection means.